This invention relates generally to electrophotographic printing machines having heat and pressure fusers, and more particularly to such a machine having a fuser release agent management (RAM) system including an external fuser roll heater and agent redistributor member.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roll or to a latent image on the photoconductive member. The toner attracted to a donor roll is then deposited on a latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate. The toner particles are heated to permanently affix the powder image to the copy substrate.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip.
The heated fuser roll is usually the roll that contacts the toner images on a substrate such as plain paper. In any event, the roll contacting the toner images is usually provided with an non-adhesive material for preventing toner offset to the fuser member. Three materials which are commonly used for such purposes are PFA.TM., Viton.TM. and silicone rubber. All of these materials, in order to maintain their non-adhesive qualities, require release agents specific to the material.
Various methods are known for applying release agent materials to a fuser member such as a heated fuser roll. One such system comprises a Release Agent Management RAM) system including a donor roll which contacts the fuser member to which the oil or release agent material is applied. The donor roll also contacts a metering roll which conveys the oil from a supply of oil to the donor roll. A blade member is provided for metering oil on the metering roll.
In low volume or desktop printers, critical machine features involve the cost and the quantity as well as the duration of required customer service operations. It is advantageous therefore to attempt to keep the number of separate customer replaceable units to a minimum, preferably to only one.
Additionally, in such printers, (especially color ones) where a RAM system is required for reliable fuser operation, conventional RAM systems ordinarily leave uneven amounts of release oil or agent on the external surface of the fuser roller, and particularly in an interdocument area of the surface of the fuser roller. This has been found to cause differential gloss defects on fused toner image copies, especially soon after cycle up when the release oil or agent rate on the fuser roller is still relatively high. This defect usually is exhibited as a low gloss band about 2 inches wide on the fused copy.
Following is a discussion of prior art, incorporated herein by reference, which may bear on the patentability of the present invention. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 5,504,566 granted to Chow et al on Apr. 2, 1996 discloses an apparatus for fusing toner images to a substrate. A Release Agent Management (RAM) system for applying silicone oil to a metering roll utilizes a pair of metering blades to improve oil uniformity on the metering roll. Thus, streaks or localized areas of excess silicone oil as the result of blade defects and/or dirt accumulation associated with a first blade, are metered or smoothed to a more uniform thickness by the second blade. To this end, the first metering blade serves to meter silicone oil to a first predetermined thickness while the second blade serves to meter oil streaks to a second predetermined thickness which is greater than the first predetermined thickness.
U.S. Pat. No. 5,212,527 granted to From et al on May 18 discloses a release agent management (RAM) system including a metering roll supported for contact with release agent material contained in a sump. A donor roll is provided for applying oil deposited thereon by the metering roll. A metering blade structure for metering silicone oil onto the metering roll has two modes of operation. In one mode, a wiping action of a metering blade meters a relatively large quantity of silicone oil to the roll surface for accommodating the fusing of color toner images. In another mode of operation, a doctoring action is effected for metering a relatively small amount of silicone oil to the roll surface for accommodating the fusing of black toner images.